Various measures for reduction of emissions of carbon dioxide (CO2) are being taken in order to deal with atmospheric pollution and global warming. In the automobile industry, the reduction of emissions of CO2 is highly expected in association with the spread of electric vehicles and hybrid electric vehicles. Thus, development of electric devices such as secondary batteries for driving motors is actively being carried out.
Since a higher capacity and cycle property are particularly required for the secondary batteries for driving motors, lithium ion secondary batteries having high theoretical energy are gaining increasing attention among other types of secondary batteries. The lithium ion secondary batteries are required to store a large amount of electricity in positive electrodes and negative electrodes by unit mass, in order to increase energy density of the lithium ion secondary batteries. The lithium ion secondary batteries highly depend on active materials used in the respective electrodes for fulfillment of such a requirement.
There are known negative electrode materials for lithium ion secondary batteries that achieve a high cycle property while keeping a high discharging capacity (for example, refer to Patent Literature 1). A negative electrode material disclosed in Patent Literature 1 contains several kinds of metallic components and alloy components having predetermined diameters, and fine carbon components having predetermined diameters and lengths.